Field-magnet for dynamo-electric machines.



Nb. 893,835. PATENTED JULY 21, 1908. A. L. GUSHMAN.

FIELD MAGNET FOB, DYNAMO ELECTRIC MACHINES APPLICATION FILED HAR.18,1907.

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FIELD-MAGNET FOB DYNAMO-ELECTRIC MACHINES.

Specification of Letters Patent.

Patented July 21, 1908.

Application filed. March 18, 1907. Serial No. 362,914.

To'all-whom a may concern; 7

Be it known that l, ABE LINCOLN CUSH- MAN, a citizen of the United'States, andv resident of Concord, in the county of Merrimack andState of New Hampshire, have invented new and useful Improvements in Field Magnets for Dynamo Electric Machines, of which the following is a specification.

My invention relates to field magnets for dynamo electric machines'and its object is to provide the improvements hereinafter set forth inthe construction of field cores, wherein enlarged or extended pole tips are provided, and wherein only so m pch of the pole tip is made removable as is'necessary to allow the field windings to be slipped on and oif the pole pieces ready wound, thus eliminating cross cuts in the pole piece so far as ossibl-e. My invention though applicable to field magnets generally, is especially intended for use in connection with variable speed motors, in which the speed variation is effected by the weakening and strengthening of the fields.

Among other objects accomplished by my invention, it is its purpose to provide .a removable pole tip which will admit of placing the field windings upon the pole pieces ready wound, of such construction thaitt o e piece and the removable pole tip shal be eliminated so far aspossible that the retaining means for the removable pole tip shall be located outside of the area of the field windings; and that the cuts between the removable part and the body of the pole piece shall be arranged approximately parallel, or at'an acute angle, with the axis of the pole niece, whereby the area of the out crossed by the lines of force shall be increased thus reducing. its reluctance by reason of all of which features obstructions are removed which would tend to cause eddy currents to flow in the pole pieces to heat the oles or distort the fields and increase the re uctance of the magnetic circuit.

While my invention is applicable to field magnets generally, I believe that in its best form it is to be employed in laminated field magnets and I will therefore address my description to a laminated magnet.

in the accompanying drawing which illustrates an embodiment of, my invention, is

shown one lamina of a laminated field 1nagnet containing my invention.

The ring 1 is provided with the several pole ieces 2 herein shown as projecting inward y from the magnetic yoke at intervals of 90. Each} pole piece 2 is made with a longitudinal recess or pocket 3 extendin throughout the length of the pole piece and into the magnetic yoke. A removable L shaped section 4 has a shank 5; fitting in the longitudinal ocket 3, and the toe 6, which forms one on of an extend d o'- flaring ole shoe. The other end 7 oi the extends or flaring ole shoe is made integral with the body of the pole piece 2. This extended pole shoe prevents the abrupt-' entrance oi the'armature wires into theifield and insures sparkless commutation when the fields are weakened to increase the speed of the motor.

Between either end 6 and 7 of the flaring pole shoe, and the body of the pole piece 2, is pgovided the notch 8 to concentrate the es of force near the tip of the pole piece, Near the end of the shank 5 of the removable section 4 of the pole piece is a retainingbolt 9 for securing the removable section in position. This retaining bolt, it will be seen, is back of and outside of the area of the field windings. stantially all cross cuts as well as the retaining means itself are eliminated from the area of the field windings, and that the cuts between the body of the pole piece and the removable section of the pole piece are approximately parallel, or at an acute angle, with the axis of the'pole piece, the large area of the cut thus provided reducing the reluctance of the magnetic circuit where it crosses said out. The cut on the side of the removable section toward the pole-tip '7, it will be seen, does not intersect the lines of force in. that side of the pole piece at all. I This result is more perfectly accomplished by the above described device than in the construction shown in my pending ap lication, Serial No. 259,293 wherein both on s of the flaring pole shoe aremade movable with the removable section, and at the same time the device is It will alsobeobserved that sub--.

equally well. adapted for slipping the field" windings on and off the pole pieces readily as When both ends of the pole shoe instead 7 of'one. end are made removable.

What I claim and desire to secure by Letters'Patent is:

1, In a field magnet, a pole piece having a longitudinal recess or pocket extending throughout the length of the pole piece, a removable polar section fitting into said recess or pocket, enlarged or extended pole tips, one on either side of the pole piece to form a flaring pole shoe, one of said extended tips being integral with 'the pole piece and the other of said extended pole tips being inte'gral with the removable section, a magnet Winding upon said pole piece, andmeans located back of the area of the magnet Winding to secure said removable section to the pole piece.

2 In a field magnet, a pole piece having a longitudinal recess or pocket extending throughout the length of the pole piece, a removable polar section fitting into said recess or pocket, enlarged or extended pole tips one on either side of the pole piece to form a flaringpole shoe, one of said extended pole tips being integral With the pole piece,

and the other of said extended poletips being inte ral With the removable section, lateral notc hes being provided between the pole tips andthe body of the pole piece, and means to -secure said removable section to the pole 3. In afield magnet, a pole piece having -a longitudinal recess or pocket extending throughout the length of the pole piece, said pole piece being provided at one side with an extension integral with tin. pole piece, to

form oneend of an extended or flaring pole of which forms the other endof the extended or flaring pole shoe, a magnet Winding upon said pole piece, and means located back of the area of the magnet Winding near the end of the shank.- for securing said removable section in position.

4. In a field magnet, a pole piece having a longitudinal recess or pocket extendin throughout the length of the pole piece, sai pole piece being provided at one side with an extension integral with the pole piece, to form one end of an extended or flaring pole shoe, and with a lateral notch between said pole shoe, and the body of the ole piece, an

. .-.-shaped removable section, 1; e shank of which fits in said recess and the toe of which forms the other end of the extended or flaring pole shoe, a lateral notch being provided between the pole shoe of said L-shape'd piece and the adjacent end of the body of the pole piece, and means for securing said removable section in position.

Signed by me at Boston, Massachusetts this 16th day of March 1907.

ABE LINCOLN CUSHMAN.

Witnesses I Ronnnr CUsHMAN, Josnrn T. BRENNAN, 

